The present invention relates to a device for preventing electromagnetic wave leakage, and more particularly to a device for preventing electromagnetic wave leakage in a microwave heating apparatus.
In microwave heating apparatus widely used, which are called "microwave heating oven", it is important to take suitable measures against microwave leakage from gaps between the apparatus body and a door because of two major reasons stated below. First is that the leakage of electromagnetic wave has harmful effect on the human body. Second is that there occur interferences or noises due to a large number of sub and/or higher harmonics included in the microwave in electronic equipment, e.g., radio and/or television receivers or computers etc.
With the above in view, there have been adopted the following four methods for preventing unnecessary radiation in the prior art. First method is to insert a metallic spring between gaps between the apparatus body and the door. Second method is to insert a conductive rubber therebetween in place of the metallic spring employed in the first method. Third method is provided between the apparatus body and the door an absorber formed by mixing ferrite absorber or ferrite powdered material into rubber or plastics. Fourth method is to form the absorber employed in the third method by mixing material having high dielectric constant into rubber or plastics, or by further mixing ferrite powdered material thereinto.
However, these conventional methods have the following drawbacks, respectively. The drawbacks with the first method is that wear or distortion is likely to occur in the spring portion, and that its effect is remarkably injured when an extraneous substance is put between the door and the apparatus body. The drawback with the second method is that there occurs deterioration or distortion produced when the conductive rubber is influenced by heat, and that its effect is greatly reduced when an extraneous substance is put between the door and the apparatus body. On the other hand, the third and fourth methods can exhibit expected effect in a sense, but are not practically acceptable because satisfactory heat-resisting properties of rubber or plastics cannot be obtained, and because a great deal of absorption materials are required for realizing a sufficient leakage preventing effect, resulting in high cost.